Large two-stroke compression-ignited internal combustion engine with fuel injection system for low flashpoint fuel and a fuel valve therefore

ABSTRACT

A large two-stroke turbocharged compression-ignited internal combustion crosshead engine with a plurality of cylinders has at least one pressure booster for each cylinder for boosting fuel pressure, two or more electronically controlled fuel valves for each cylinder with an inlet of the two or more electronically controlled fuel valves being connected to an outlet of the at least one pressure booster. An electronic control unit is connected to the at least one pressure booster and the two or more electronically controlled fuel valves. The electronic control unit is configured to determine a start time for a fuel injection event, activate the at least one pressure booster ahead of the determined start time and pen the two or more electronically controlled fuel valves at the determined start time.

TECHNICAL FIELD

The disclosure relates to large slow-running two-strokecompression-ignited internal combustion crosshead engines with a fuelinjection system for injecting a low flashpoint fuel into the combustionchambers.

BACKGROUND

Large two-stroke uniflow turbocharged compression-ignited internalcombustion crosshead engines are typically used in propulsion systems oflarge ships or as prime mover in power plants. The sheer size, weightand power output renders them completely different from commoncombustion engines and places large two-stroke turbochargedcompression-ignited internal combustion engines in a class forthemselves.

Large two-stroke turbocharged compression-ignited internal combustionengines of the crosshead type are typically used in propulsion systemsof large ships or as prime mover in power plants.

Large two-stroke compression-ignited internal combustion engines areconventionally operated with a liquid fuel such as e.g. fuel oil orheavy fuel oil but increased focus on environmental aspects has led tothe development towards using alternative types of fuel such as gas,methanol, coal slurry, petroleum coke and the like. One group of fuelsthat is in increasing demand are low flashpoint fuels.

Many low flashpoint fuels, such as methanol, ethanol, LPG, DME orbiofuel, naphta, gasoline (petrol), crude gasoline, crude oil arerelatively clean fuels that result in significantly lower levels ofsulfurous components, NOx and CO2 in the exhaust gas when used as fuelfor a large low-speed uniflow turbocharged two-stroke internalcombustion engine when compared with e.g. using heavy fuel oil as fuel.

However, there are problems associated with using a low flashpoint fuelsin a large low-speed uniflow turbocharged two-stroke internal combustionengine. One of those problems is the low flashpoint, which causessignificant problems if low flashpoint fuel leaks into one of the othersystems of the engine and mixes with another fluid, such as e.g. thelubrication oil system. Low flashpoint fuel, is inherently easy toignite and vapors thereof can easily form explosive mixtures. Thus,should low flashpoint find its way into another system of the engine itis necessary to stop the engine operation for safety reasons and toclean or replace all of the liquid in such a system, a costly andcumbersome affair for the operator of the engine.

The timing of the fuel injection highly affects the combustion pressurein a Diesel engine (compression-ignited engine) and therefore the timingof the fuel injection in a compression-ignited engine needs to becontrolled very accurately.

It is known in the art to provide large two-stroke compression ignitedinternal combustion engines with a common rail type system that storesand distributes the gas at the required injection pressure of typicallyseveral hundred bar (depending on the type of gas and the enginerequirements), with accumulators close to the fuel valves. The commonrail type system is connected to two or three fuel injection valves inthe cylinder cover of each cylinder. The fuel injection valves areelectronically controlled and fuel injection is timed by electronically(the signal originates in an electronic control unit but the actualsignal to the fuel valve is typically a hydraulic signal, i.e.electronic signal is converted to a hydraulic signal between theelectronic control unit and the fuel valve) controlling the time(relative to the engine cycle) at which the fuel injection valve isopened.

The amount of fuel admitted to a cylinder in one injection event iselectronically controlled by the length of the time interval from theopening of the fuel valve to the closing of the fuel valve. In order toensure safety against ill-timed and/or unlimited injection the so-calledwindow valve is provided between the accumulator and the fuel valve.Thus the maximum amount of fuel that can be injected when e.g. a fuelvalve is stuck in its open position is the amount of fuel gas that ispresent in the system between the window valve and the fuel valve, whichis a relatively small and therefore safe amount.

The known common rail type gaseous fuel supply system for largetwo-stroke compression-ignited internal combustion engines havedisadvantages when operating on LPG or any other similar low flashpointfuel with a relatively high compressibility. The injection pressure forLPG needs to be as high as 600 bar, which means that the common railsystem including all valves, accumulators, pipes, etc., needs be laidout for this high pressure. Furthermore, the safety concept with thewindow valves is not well suited for dense gas like LPG, since firstlythe gas channels between window valve and fuel valve need to have a verysmall volume and secondly, monitoring of the gas channel pressurenecessary to ensure detection of leakages is made very difficult due tohigh frequency oscillation excited from closing of the window valve.

It is also known in the art to use booster pumps and fuel pressurecontrolled fuel valves for injecting liquid gas, such as e.g. LPG. Thisconcept has the problem associated therewith that the compressibility ofLPG is rather large and dependent on pressure, temperature and gascomposition. Hence, the delay between the actuation of the pressurebooster and the actual gas injection is dependent on those parameters,which will make engine control, i.e. injection amount and particularlyinjection timing, very difficult. This is a significant problem, sinceinjection timing is critical in compression-ignited engines.

There is therefore a need to provide a fuel supply system for LPG andsimilar low flashpoint fuels that is safe, inexpensive and providesaccurate control of the timing of the fuel admission into the cylinders.

SUMMARY

The aspects of the disclosed embodiments are directed to provide a largetwo-stroke turbocharged compression-ignited internal combustioncrosshead engine that overcomes or at least reduces the problemindicated above.

The foregoing and other objects are achieved by the features of theindependent claims. Further implementation forms are apparent from thedependent claims, the description and the figures.

According to a first aspect there is provided a large two-stroketurbocharged compression-ignited internal combustion crosshead enginecomprising:

-   a plurality of cylinders,-   at least one pressure booster for each cylinder for boosting fuel    pressure,-   two or more electronically controlled fuel valves for each cylinder    with an inlet of said two or more electronically controlled fuel    valves being connected to an outlet of said at least one pressure    booster,-   an electronic control unit operably connected to said at least one    pressure booster and said two or more electronically controlled fuel    valves, said electronic control unit being configured to:

determine a start time for a fuel injection event,

activate said at least one pressure booster ahead of the determinedstart time,

open the two or more electronically controlled fuel valves at thedetermined start time.

By providing a fuel supply system with a pressure booster that booststhe pressure delivered to the fuel valve from a moment in time in theengine cycle sufficiently in advance of the earliest possible start ofthe fuel injection event until the latest possible end of the fuelinjection event combined with a fuel valve in which the opening andclosing of the fuel valve is electronically controlled and not dependentof the pressure of the supply fuel, a fuel supply system can be providedwith the following advantages:

-   -   no large gas accumulator is needed,    -   no windows valve is needed that in the past has caused many        problems    -   injection timing and duration can be accurately controlled    -   no need for a large gas accumulator,    -   online check for leaking GI injection valve is easily obtained        by monitoring the booster pressure,    -   booster pressure can be measured on the hydraulic side        which is much simpler and easier that on the fuel side,

-   despite having a common rail derived injection valve, still    injection pressure control and shaping is possible,

-   in case of fuel valve leakage no gas can entrain into the gas supply    side.

According to a first possible implementation of the first aspect theelectronic control unit is configured to determine said start time foreach cylinder of said plurality of cylinders for each engine cycle.

According to a second possible implementation of the first aspect theelectronic control unit is configured to activate the at least onepressure booster ahead of the determined start time by a time spandetermined by said electronic control unit.

According to a third possible implementation of the first aspect theelectronic control unit is configured use a fixed time span, a time spanobtained from a lookup table stored in said electronic control unit or atime span determined by said electronic control unit using an algorithmstored in said electronic control unit.

According to a fourth possible implementation of the first aspect theopening and closing of said electronically controlled fuel valves iscontrolled by a control signal from said electronic control unit.

According to a fifth possible implementation of the first aspect theopening and closing of said electronically controlled fuel valves isindependent from the pressure in the fuel supplied to the electronicallycontrolled fuel valves.

According to a sixth possible implementation of the first aspect theelectronic control unit is configured to determine the duration of afuel injection event and wherein the electronic control unit isconfigured to close said at least two electronically controlled fuelvalves at the end of said duration and configured to deactivate said atleast one pressure booster at the end of said duration.

According to a seventh possible implementation of the first aspect eachfuel valve comprises an elongated valve housing and wherein saidpressure booster is disposed inside said elongated valve housing.

According to an eighth possible implementation of the first aspect thepressure booster comprises a pump piston (80) received in a first borein said valve housing with a pump chamber in said first bore on one sideof said pump piston, an actuation piston received in a second bore insaid valve housing with an actuation chamber in said second bore (84) onone side of said actuation piston, said pump piston being connected tosaid actuation piston to move in unison therewith, said actuationchamber being connected to an actuation fluid port, said pump chamberhaving an outlet connected to a fluidic connection to the nozzle holesof the nozzle of said fuel valve.

According to a ninth possible implementation of the first aspect thefuel valve is provided with a valve needle that controls the flow offuel to nozzle holes of the nozzle of said fuel valve, the position ofsaid valve needle preferably being controlled by a control signal andnot by the fuel pressure.

According to a tenth possible implementation of the first aspect thepressure booster and said fuel valve are adapted to operate with a lowflashpoint fuel, preferably a low flashpoint fuel that is morecompressible than fuel oil.

According to an eleventh possible implementation of the first aspect theengine further comprises a conduit for supplying sealing liquid to aclearance between a bore of the pressure booster and a pump pistonslidably received in said bore of the pressure booster.

According to a twelfth possible implementation of the first aspect theengine further comprises a conduit for supplying sealing liquid to aclearance between a bore of the fuel valve and valve needle slidablyreceived in said bore of the fuel valve.

According to a second aspect, there is provided fuel valve for injectinglow flashpoint liquid fuel into the combustion chamber of a large slowrunning two-stroke turbocharged self-igniting internal combustionengine, said fuel valve comprising:

-   an elongated fuel valve housing with a rear end and a front end,-   a nozzle with a plurality of nozzle holes, said nozzle being    disposed at the front end of said elongated valve housing,-   a fuel inlet port in said elongated valve housing for connection to    a source of pressurized liquid low flashpoint fuel,-   an actuation fluid port in said elongated fuel valve housing for    connection to a source of actuation fluid,-   an axially displaceable valve needle slidably received in a    longitudinal bore in said fuel valve, said valve needle having a    closed position and an open position and said valve needle being    biased towards said closed position,-   said valve needle allowing flow of fuel from a fuel cavity to said    plurality of nozzle holes when the valve needle is in its open    position and said valve needle preventing flow of fuel from said    fuel cavity to said plurality of nozzle holes when the valve needle    is in its closed position,-   said valve needle being operably connected to a needle actuation    piston with a pressure surface of said actuation piston facing a    needle actuation chamber in said fuel valve, said needle actuation    chamber being fluidically connected to a needle actuation fluid port    in said fuel valve,-   a pump piston received in a first bore in said valve housing with a    pump chamber in said first bore on one side of said pump piston,-   an actuation piston received in a second bore in said valve housing    with an actuation chamber in said second bore (84) on one side of    said actuation piston, said pump piston being connected to said    actuation piston to move in unison therewith,-   said actuation chamber being connected to an actuation fluid port,-   said pump chamber having an outlet fluidically connected to said    fuel cavity and an inlet fluidically connected to said fuel inlet    port.

By providing the fuel valve with a pressure booster and a valve needlewhere lift is controlled by an actuation pressure and not by fuelpressure, a fuel valve is created that can handle low flashpoint fuelsthat are more compressible than regular fuel oil without the need for acommon rail system.

According to a first possible implementation of the second aspect thefuel valve comprises a sealing liquid inlet port for connection to asource of pressurized sealing liquid, and a conduit connecting saidsealing liquid inlet port (70) to said first bore for sealing said pumppiston in said first bore.

According to a second possible implementation of the second aspect thefuel valve further comprises a conduit connecting said sealing liquidinlet port to said longitudinal bore for sealing said valve needle insaid longitudinal bore.

According to a third possible implementation of the second aspect theeffective pressure area of said pump piston (80) is smaller than theeffective pressure area of said actuation piston.

According to a fourth possible implementation of the second aspect thenozzle is part of a body that is secured to the front of said elongatedvalve housing.

According to a fifth possible implementation of the second aspect theinlet is located in said pump piston.

According to a sixth possible implementation of the second aspect afirst one-way valve is provided in said inlet, said first one-way valvebeing configured to allow flow of low flashpoint fuel through said inletinto said pump chamber and to prevent flow from said pump chamber intosaid inlet.

According to a seventh possible implementation of the second aspect theoutlet of said pump chamber is connected to said fuel cavity by one ormore fuel channels.

According to an eighth possible implementation of the second aspect asecond one-way valve is provided in said one or more fuel channels, saidsecond one-way valve being configured to allow flow of low flashpointfuel from said pump chamber to said fuel cavity and to prevent flow fromsaid fuel cavity to said pump chamber.

According to a ninth possible implementation of the second aspect thevalve needle rests on a valve seat in said closed position and saidvalve needle has lift from said valve seat in said open position.

According to a third aspect, there is provided a fuel valve forinjecting low flashpoint liquid fuel into the combustion chamber of alarge slow running two-stroke turbocharged self-igniting internalcombustion engine, said fuel valve comprising:

-   an elongated fuel valve housing with a rear end and a front end,-   a nozzle with a plurality of nozzle holes, said nozzle being    disposed at the front end of said elongated valve housing,-   a fuel inlet port in said elongated fuel valve housing for    connection to a source of pressurized liquid low flashpoint fuel,-   an actuation fluid port in said elongated fuel valve housing for    connection to a source of actuation fluid,-   an axially displaceable valve needle slidably received in a    longitudinal bore in said fuel valve, said valve needle having a    closed position and an open position and said valve needle being    biased towards said closed position,-   said valve needle allowing flow of fuel from a fuel cavity to said    plurality of nozzle holes when the valve needle is in its open    position and said valve needle-   preventing flow of fuel from said fuel cavity to said plurality of    nozzle holes (56) when the valve needle is in its closed position,-   a pump piston received in a first bore in said valve housing with a    pump chamber in said first bore on one side of said pump piston,-   an actuation piston received in a second bore in said valve housing    with an actuation chamber in said second bore on one side of said    actuation piston, said pump piston being connected to said actuation    piston to move in unison therewith,-   said actuation chamber being connected to an actuation fluid port,-   said pump chamber having an outlet fluidically connected to said    fuel cavity and an inlet fluidically connected to said fuel inlet    port,-   a sealing liquid inlet port for connection to a source of    pressurized sealing liquid,-   a conduit connecting said sealing liquid inlet port to said first    bore for sealing said pump piston in said first bore,-   a conduit connecting said sealing liquid inlet port to said    longitudinal bore at a first position along the length of said    longitudinal bore for sealing said valve needle in said longitudinal    bore,-   a conduit connecting the low flashpoint fuel supply port to the said    longitudinal bore at a second position along the length of said    longitudinal bore, said second position being closer to said fuel    cavity than said first position.

By providing a conduit connecting the low flashpoint fuel supply port tothe said longitudinal bore at a second position, a position being closerto said fuel cavity than said first position of the sealing liquid, thehigh sealing oil does not have to seal against the boosted fuel pressure(injection pressure) of several hundred bar (which would require an evenhigher sealing liquid pressure). Instead, the fuel is allowed to leakback to the fuel supply system at a pressure which is significantlylower that the injection pressure. Thus, the high pressure fuel area inthe clearance between the valve needle and the longitudinal bore ispunctured by the connection to the fuel supply port and the sealingliquid needs only to seal against the much lower fuel supply pressure.

According to a first possible implementation of the third aspect thevalve needle rests on a valve seat in said closed position and saidvalve needle has lift from said valve seat in said open position.

According to a second possible implementation of the third aspect thenozzle has a nozzle body that is secured to the front of said elongatedvalve housing.

According to a third possible implementation of the third aspect thevalve seat is located in the tip of said nozzle.

According to a fourth possible implementation of the third aspect thelongitudinal bore is formed at least partially in said nozzle body.

According to a fifth possible implementation of the third aspect lift ofsaid valve needle is controlled by the fuel pressure.

These and other aspects will be apparent from the embodiments describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, the aspectsand possible implementations will be explained in more detail withreference to the example embodiments shown in the drawings, in which:

FIG. 1 is an elevated front view of a large two-stroke diesel engineaccording to an example embodiment,

FIG. 2 is an elevated side view of the large two-stroke engine of FIG.1.

FIG. 3 is a diagrammatic representation the large two-stroke engineaccording to FIG. 1, and

FIG. 4 is a diagrammatic representation of the fuel injection system forinjecting a low flashpoint fuel into the engine of FIGS. 1 and 2,

FIG. 5 is an elevated view of a fuel valve for according to anembodiment,

FIGS. 6 to 9 are sectional views of the fuel valve of FIG. 5,

FIG. 10 illustrates an alternative nozzle for the fuel valve of FIG. 5,and

FIG. 11 is a flow chart illustrating a method for injecting lowflashpoint fuel into the engine of FIGS. 1 and 2.

DETAILED DESCRIPTION

In the following detailed description, an internal combustion enginewill be described with reference to a large two-stroke low-speedturbocharged compression-ignited internal combustion engine withcrossheads in the example embodiments, but it is understood that theinternal combustion engine could be of another type, such as atwo-stroke Otto, a four-stoke Otto or Diesel, with or withoutturbocharging, with or without exhaust gas recirculation.

FIGS. 1, 2 and 3 show a large low-speed turbocharged two-stroke dieselengine with a crankshaft 8 and crossheads 9. FIG. 3 shows a diagrammaticrepresentation of a large low-speed turbocharged two-stroke dieselengine with its intake and exhaust systems. In this example embodimentthe engine has six cylinders in line. Large low-speed turbochargedtwo-stroke diesel engines have typically between four and fourteencylinders in line, carried by a cylinder frame 23 that is carried by anengine frame 11. The engine may e.g. be used as the main engine in amarine vessel or as a stationary engine for operating a generator in apower station. The total output of the engine may, for example, rangefrom 1,000 to 110,000 kW.

The engine is in this example embodiment a compression-ignited engine ofthe two-stroke uniflow type with scavenge ports 18 at the lower regionof the cylinder liners 1 and a central exhaust valve 4 at the top of thecylinder liners 1. The scavenge air is passed from the scavenge airreceiver 2 to the scavenge ports 18 of the individual cylinders 1. Apiston 10 in the cylinder liner 1 compresses the scavenge air, fuel isinjected through fuel valves 50 in the cylinder cover 22, combustionfollows and exhaust gas is generated.

When an exhaust valve 4 is opened, the exhaust gas flows through anexhaust duct associated with the cylinder 1 into the exhaust gasreceiver 3 and onwards through a first exhaust conduit 19 to a turbine 6of the turbocharger 5, from which the exhaust gas flows away through asecond exhaust conduit via an economizer 20 to an outlet 21 and into theatmosphere. Through a shaft, the turbine 6 drives a compressor 7supplied with fresh air via an air inlet 12. The compressor 7 deliverspressurized scavenge air to a scavenge air conduit 13 leading to thescavenge air receiver 2. The scavenge air in the scavenge air conduit 13passes an intercooler 14 for cooling the scavenge air.

The cooled scavenge air passes via an auxiliary blower 16 driven by anelectric motor 17 that pressurizes the scavenge air flow when thecompressor 7 of the turbocharger 5 does not deliver sufficient pressurefor the scavenge air receiver 2, i.e. in low or partial load conditionsof the engine. At higher engine loads the turbocharger compressor 7delivers sufficient compressed scavenge air and then the auxiliaryblower 16 is bypassed via a non-return valve 15.

The engine is operated with a low flashpoint fuel, such as e.g. LPG,methanol or naphta and supplied by a low flashpoint fuel supply system30 in liquid or supercritical form at a substantially stable pressureand temperature. However, depending on the details of the low flashpointfuel supply system and the type of gas supplied slight variations intemperature and pressure are unavoidable. Further, slight variations inthe composition of the low flashpoint fuel can also occur.

The low flashpoint fuel supply system 30 supplies the fuel injectionvalves 50 with low flashpoint fuel at relatively low supply pressure(e.g. 8 to 100 Bar pressure) via a supply conduit 31.

FIG. 4 is a diagram showing the fuel injection system that receives thelow flashpoint fuel via the supply conduit 31. The fuel injection systemcomprises a pressure booster 40 for pressurizing the fuel to theinjection pressure. The pressure booster 40 that is hydraulicallyactuated under control of a first control valve 41 and fuel valves 50that are hydraulically actuated under control of a second control valve45.

The diagram in FIG. 4 shows the fuel injection system for a singlecylinder 1, with one pressure booster 40 and three fuel injection valves50. Instead of three, there could also be two fuel valves 50 for eachcylinder 1. Each cylinder 1 will require a pressure booster 40 supplyingtwo or three fuel valves 50.

The pressure booster 40 comprises a large diameter plunger connected toa smaller diameter plunger to move in unison therewith. The largediameter plunger and the small diameter plunger are received inrespective matching bores in the housing of the pressure booster 40. Thelarge diameter plunger faces an actuation chamber that is supplied withhigh pressure hydraulic fluid or with tank under control of the firstcontrol valve 41.

The small diameter plunger faces a pump chamber that is connected to thefuel supply line 31 via a one-way valve and to a high-pressure fuelsupply line 35 for the delivery of high pressure fuel to the fuel valves50. A one-way valve prevents backflow of fuel from the high-pressurefuel supply line 35 to the pump chamber. The pressure in the fuel in thesupply line 31 is sufficient to cause the pressure booster 40 to make areturn stroke when the actuation chamber is connected to tank. Aposition sensor 34 senses the position of the large and small diameterplungers. Sealing liquid, such as sealing oil is supplied to theclearance between the large diameter piston and the bore in which it isreceived for preventing fuel leaking into the pressure chamber andmixing with the hydraulic fluid. A pressure sensor 36 senses thepressure in the high-pressure fuel supply line 35.

In the present embodiment the first control valve 41 comprises apreferably proportional first hydraulically controlled three-way valve42. The first three-way valve 42 is connected to the actuation chambervia a actuation conduit 44, to a source of high-pressure hydraulic fluidand to tank. The first three-way valve 42 is configured to connect theactuation chamber selectively to tank or to the source of high-pressurehydraulic fluid. Since the first hydraulically controlled three-wayvalve 42 is in an embodiment a proportional valve capable of assumingany intermediate position between connection to the source ofhigh-pressure hydraulic fluid and tank. The position of the firstthree-way valve 42 is controlled by a first smaller two-way valve 43 andthe position of the first smaller two-way valve 43 is electronicallycontrolled. The first smaller two-way valve 43 is connected to anelectronic control unit 25 via a first signal cable 26. In anembodiment, the first control valve 41 is under command of a separateelectronic control unit that is mainly configured for maintaining safetyand will deactivate the pressure booster when a safety issue, such ase.g. a gas leak, has been detected. Alternatively, the first controlvalve is connected to a source of high pressure hydraulic fluid that iscontrolled by an engine safety system.

The high-pressure fuel supply line 35 is split up into threehigh-pressure fuel supply lines 35-1, 35-2, 35-3, i.e. one high-pressurefuel supply line for supplying each fuel valve 50 with high-pressure lowflashpoint fuel. In an embodiment with two fuel valves 50 per cylinderthe high-pressure fuel supply line 35 will be split in two lines.

Each fuel valve 50 is connected to a supply of sealing oil via a sealingoil supply line 36 and with a sealing oil return line. The flow sealingoil through the fuel valve 50 is in an embodiment relatively large sothat the sealing oil also acts as a cooling medium for the fuel valve50.

Each fuel valve 50 is connected to a fuel valve actuation signal conduit48. The pressure in the fuel valve actuation signal conduit 48 iscontrolled by a second control valve 45 that comprises in an embodimenta second hydraulically controlled proportional three-way valve 46 and asecond smaller electronically controlled two-way valve 47. The secondhydraulically controlled three-way valve 46 is preferably a proportionalvalve and is configured to connect the actuation signal conduit 48 to asource of high-pressure hydraulic fluid or to tank. Since the secondhydraulically controlled three-way valve 46 is in an embodiment aproportional valve it is capable of assuming any intermediate positionbetween connection to the source of high-pressure hydraulic fluid andtank. The position of the second three-way valve 46 is controlled by asecond smaller two-way valve 47 and the position of the second smallertwo-way valve 47 is electronically controlled. The second smallertwo-way valve 47 is connected to the electronic control unit 25 via athird signal cable 28. The electronic control unit 25 is informed of theposition of the second three-way valve 46 via a second signal cable 27.

The electronic control unit 25 is in receipt of signals from varioussensors via signal cables that are illustrated in FIG. 4 as interruptedlines. The signals from the various sensors include e.g. scavengingpressure and temperature, exhaust pressure and temperature and crankangle and speed, although it is noted that this list is not exhaustiveand will depend on the construction of the engine, for example whetherit includes exhaust gas recirculation or not, whether it includes aturbocharger or not, etc. The electronic control unit 25 controls thefuel injection valves 50 i.e. the electronic control unit determineswhen the fuel valve 31 is open and determines the duration of theopening time. The electronic control unit 25 also controls the operationof the pressure booster 40.

The timing of the fuel injection highly affects the combustion pressurein the large two-stroke turbocharged diesel engine (compression-ignitedengine). The timing of the opening of the fuel valves 50 relative to thecrankshaft angle or relative to the engine cycle largely determines thecombustion pressure. The duration of the opening of the fuel valves 50determines the amount of fuel admitted to the cylinders 1, withincreasing duration leading to increasing amount of fuel being admittedto the cylinders 1.

The electronic control unit 25 is configured to control the timing ofthe opening of the fuel valves by an electronic signal to the controlvalve 45 via the third signal cable 28. Upon receipt of the signal theelectronic control valve switches position and connects the actuationsignal conduit 48 to the source of high-pressure hydraulic fluid. Thehigh pressure in the actuation signal conduit 48 opens the fuel valve50.

In order to ensure that the fuel with a sufficient pressure forinjection is ready to be injected when the fuel valve 50 opens, theelectronic control unit 25 activates the pressure booster 40 beforeopening the fuel valve 50. The advanced activation of the pressurebooster 40 is necessary to build up pressure in the relativelycompressible low flashpoint fuel. The electronic control unit 25 can beconfigured to activate the pressure booster 40 in advance of opening thefuel valve 55 by a fixed, predetermined length of time, obtained e.g.from test runs or the electronic control unit 25 can be configured todetermine the appropriate time between activation of the pressurebooster 40 and opening the fuel valve 50 using an algorithm stored inthe electronic control unit 25. The algorithm may in an embodiment takee.g. the engine load, the engine speed and fuel properties into account.

By timely activating the pressure booster 40, the pressure in thehigh-pressure supply lines 35-1, 35-2 and 35-3 is build up to theappropriate injection pressure of several hundred bar (can be as much a600 bar) before the electronic control unit 25 instructs the fuel valves50 to open.

The electronic control unit 25 is configured to determine the durationof the opening of the fuel valves based on various parameters, such ase.g. engine load, engine speed and fuel properties and the electroniccontrol unit closes the fuel valves 50 when the required duration of theinjection event has been reached. Simultaneously, the electronic controlunit 25 instructs the pressure booster 40 to make a return stroke, i.e.to refill the pump chamber and deplete the actuation chamber byinstructing the first control valve 41 to connect the actuation chamberto tank, whereupon the pressure in the fuel supply line 31 causes thepressure booster 40 to make a return stroke filling the pump chamberwith fuel and emptying the actuation chamber for hydraulic fluid.

In the embodiment above the pressure booster 40 and the fuel valve 50are separate physical units. In an embodiment the pressure booster 40 isan integral part of the fuel valve 50.

An embodiment of a fuel valve 50 with such an integrated pressurebooster is shown in FIGS. 5 to 9.

FIG. 5 is a perspective view of the fuel valve 50 with its elongatedvalve housing 52, a nozzle 54 secured to the front end of the elongatedvalve housing 52. The nozzle 54 is provided with a plurality of nozzleholes 56 for creating jets of fuel into the combustion chamber. Thenozzle 54 is removably secured to the elongated valve housing 52, sothat it can be easily replaced if the nozzle 54 should fail or be wornout.

FIGS. 6, 7, 8 and 9 show different sectional views of the fuel valve 50.The fuel valve 50 has an elongated valve housing 52 with a rearmost endand a nozzle 54 at its front end. The nozzle 54 is a separate body thatis attached to the front end of the valve housing 52. The rearmost endof the valve housing 52 is provided with a plurality of ports, includinga control port 86, an actuation fluid port 78 and a gas leak detectionport (not shown). The rearmost end is enlarged to form a head thatprotrudes from the cylinder cover when the fuel valve 50 is mounted inthe cylinder cover. In the present embodiment, the fuel valves 50 areplaced around the central exhaust valve 4, i.e. relatively close to thewall of the cylinder liner. The elongated valve housing 52 and the othercomponents of the fuel injection valve 50, as well as the nozzle are inembodiment made of steel, such as e.g. tool steel or stainless steel.

The nozzle 54 is provided with nozzle holes that are connected to theinterior in the nozzle 54 and the nozzle holes are arranged in differentdirections in order to distribute the fuel in the combustion chamber.The nozzle holes are directed away from the cylinder liner which isrelatively nearby due to the location of the fuel valve 50 in thecylinder head. The nozzles holes are arranged in the tip 56 of thenozzle 54. Further, the nozzle holes are directed such that they areroughly in the same direction as the direction of the swirl of thescavenge air in the combustion chamber caused by the configuration ofthe scavenge ports (this swirl is a well-known feature of largetwo-stroke turbocharged internal combustion engines of the uniflowtype).

The nozzle 54 is connected to the front end of the valve housing 52 witha sleeve 57 securing and surrounding a portion of the nozzle body 55,surrounding an intermediate section 53 and surrounding a distal portionof the elongated valve housing 52. The nozzle body 55 is provided with alongitudinal bore in which the valve needle 61 is received. Thelongitudinal bore has a diameter that is larger than the diameter of thevalve needle 61 in the portion of the longitudinal bore closest to thetip 56. The space between the longitudinal bore and the valve needle 61forms a fuel cavity 58. An intermediate section of the longitudinal borehas a very small clearance with the valve needle 61. The portion of thelongitudinal bore in the nozzle body 55 most distant from the tip 56 ofthe nozzle 54 has an enlarged diameter matching and an enlarged diameterportion of the valve needle 61. The enlarged diameter portion of thevalve needle 61 forms a needle actuation piston 62 with a pressuresurface of the needle actuation piston 62 facing a needle actuationchamber 88 in the nozzle 54. The needle actuation chamber 88 isfluidically connected to the control port 86 via a control conduit 87.

The enlarged diameter section of the longitudinal bore is aligned with aspring chamber 96 in the intermediate section 53. The spring chamber 96is aligned with a longitudinal bore in the elongated valve housing 52.The distal section of the longitudinal bore in the elongated valvehousing 52 closest to the distal end of the elongated valve housing 52has a diameter that corresponds to the diameter and the spring chamber96. A helical wire spring 68 extends between distal section of thelongitudinal in the elongated valve housing 52 and the enlarged diametersection 62 of the valve needle 61. The valve needle 61 is resilientlybiased towards its closed position by the pre-tensioned helical spring68. The helical spring 68 is a helical wire spring that is received in aspring chamber 96 in the elongated fuel valve housing 52. The helicalwire spring 68 biases the valve needle 61 towards the tip 56 of thenozzle 54, i.e. to its closed position. In the closed position of thevalve needle 61 the, preferably conical, tip of the valve needle 61abuts with a preferably conical seat 63 in the tip 56 of the interior ofthe nozzle 54 and closes the fluidic connection between the fuel cavity58 and the nozzle holes. The fluidic connection between the fuel cavity58 and the nozzle holes is established when the valve needle 61 haslift, i.e. when the valve needle 61 is forced towards the proximate endof the fuel valve 50 against the bias of the helical spring 68. Thevalve needle 61 gets lift when the needle actuation chamber 88 ispressurized.

A spring guide 69 extends concentrically in the spring chamber 96 forguiding the helical spring 68. The proximate end of the spring guide 69is sealingly received in the longitudinal bore in the elongated valvehousing 52.

The axially displaceable valve needle 61 is slidably received with anarrow clearance in a longitudinal bore in the nozzle body 55, andlubrication between the axially displaceable valve needle 61 and thelongitudinal bore is critical. Hereto, pressurized sealing liquid isdelivered to the clearance between the longitudinal bore in the valveneedle via a conduit (channel) 93. The channel 93 connects the clearancebetween the valve needle 61 and the longitudinal bore to a sealingliquid inlet port 70, which in turn can be connected to the source ofpressurized sealing liquid. The connection between the clearance and thechannel 93 includes a transverse bore 99 (FIG. 8) in the valve needle 61that connects to an axial bore 97 (FIG. 8) in the valve needle 61 thatextends all the way through the enlarged diameter section that forms theneedle actuation piston 62 to the spring chamber 96. The channel 93connects to the spring chamber 96 and supplies the spring chamber 96with pressurized sealing liquid. In order to allow a substantial flow ofsealing liquid through the spring chamber 96 so that the sealing liquidmay act as a cooling medium the spring chamber 96 is connected via abore to a sealing liquid outlet port 95. The sealing liquid preventsleakage of low flashpoint fuel through the clearance between the valveneedle 61 and the axial bore and provides cooling to the fuel valve 50.Further, the sealing liquid, which is preferably an oil, provides forlubrication between the valve needle 61 and the longitudinal bore.

The elongated valve housing 52 is provided with a fuel inlet port 76 forconnection to a source of pressurized low flashpoint liquid fuel 60, forexample via the low flashpoint liquid fuel supply conduit 31. The fuelinlet port 76 connects to a pump chamber 82 in the valve housing 52 viaa conduit 73 in a pump piston 80 and a one-way valve 89. The one-wayvalve 89 (suction valve) is provided in the pump piston 80 at an inlet71 of the conduits 73. The one-way valve 89 is a spring loaded poppetvalve that ensures that liquid low flashpoint fuel can flow from thefuel inlet port 76 via conduit 73 to the pump chamber 82, but not in theopposite direction. The fluidic connection between the conduit 73 in thepump piston 80 and the fuel inlet port 76 in the elongated housing 52 isestablished by a receded area 74 in the pump piston 80 that in axialdirection overlaps with the bore in the elongated housing 52 that formsthe fuel inlet port 76.

The pump piston 80 is slidably and sealingly received in a first bore 81in the elongated fuel valve housing 52 with a pump chamber 82 in thefirst bore 81 on one side of the pump piston 80. An actuation piston 83is slidably and sealingly received in a second bore 84 in the valvehousing 52 with an actuation chamber 85 in the second bore 84 on oneside of the actuation piston 83. The pump piston 80 is connected to theactuation piston 83 to move in unison therewith, i.e. the pump piston 80and the actuation piston 83 can slide in unison their respective bores81,84. In the present embodiment the pump piston 80 and the actuationpiston 83 are formed as a single body. However, it is noted that thepump piston 80 and the actuation piston 83 can be separateinterconnected bodies.

The actuation chamber 85 is fluidically connected to an actuation fluidport 78. The first control valve 41 controls the flow pressurizedactuation liquid to and from the actuation fluid port 78 and thereby toand from to the actuation chamber 85.

A lead time before the start of injection event, the electronic controlunit 25 commands the first control valve 41 to allow high pressureactuation liquid into the actuation chamber 85. At this moment theactuation piston 83 and pump piston 80 combination is in the positionshown in FIG. 6. The pressurized actuation liquid in the actuationchamber 85 acts on the actuation piston 83, thereby creating a forcethat urges the pump piston 80 into the pump chamber 82. Thereby, thepressure of the low flashpoint liquid fuel in the pump chamber 82increases. In an embodiment the diameter of the actuation piston 83 islarger than the diameter of the pump piston 80 and thus the pressure inthe pump chamber 82 will be correspondingly higher than the pressure inthe actuation chamber 85 and the combination of the actuation piston 83and pump piston 80 acts as a pressure booster.

One or more fuel channels 79 fluidically connect the pump chamber 82 tothe fuel cavity 58 and thereby to the valve seat that is located at thebottom of the fuel cavity 58. A one-way valve 90 is placed between thefuel channels 79 and the pump chamber 82. The outlet 66 of the pumpchamber 82 is connected to the inlet of the one-way valve 90. Theone-way valve 90 comprises a valve member slidably received in an axialbore in the elongated valve housing 52 and the valve member isresiliently biased towards its seat, i.e. towards its closed positionand prevents backflow of fuel from the fuel channel 79 into the pumpchamber 82. The pressurized fluid in the actuation chamber 85 will causethe actuation piston 83 and the pump piston 80 to move downwards(downwards as in FIGS. 6 to 9) as shown in FIG. 7. The pressure in thepump chamber 82 will after a short compression phase be the product ofthe ratio between the effective pressure area of the pump piston 80 andthe effective pressure area of the actuation piston 83 and the pressurein the actuation chamber 85. At this moment the pressure in theactuation chamber 85 will be substantially equal to the pressure of thesource of high pressure fluid. With an effective pressure surface ratioof e.g. 2.5:1 and a supply pressure of the hydraulic system of 200 barthe pressure in the fuel in pump chamber will be approximately 500 barat the end of the compression phase. Thus, the combination of theactuation piston 83 and pump piston 80 acts as a pressure booster.

The electronic control unit 25 pressurizes the actuation chamber 85before the start of the fuel injection by a lead time sufficient toensure that the pressure in the pump chamber 82 has reached the requiredinjection pressure of e.g. 500 bar. The electronic control unit 25determines when the valve needle 61 needs to lift and thus when the fuelinjection commences. The valve needle 61 is configured to move in thedirection away from the nozzle 54 to obtain lift, and towards the nozzle54 to reduce lift. The valve needle 61 gets lift when the valveactuation chamber 88 is pressurized. The electronic control unit 25instructs the second control valve 45 to connect the fuel valveactuation signal conduit 48 to the source of high pressure hydraulicfluid at the moment in the engine cycle when the fuel injection has tocommence. The fuel valve actuation signal conduit 48 is connected to thecontrol port 86 and the high pressure fluid reaches the valve actuationchamber 88 via control conduit 87. When the valve needle 61 has liftfrom its seat it allows flow of low flashpoint liquid fuel from the fuelcavity 58 through the nozzle holes into the combustion chamber.

The electronic control unit 25 ends an injection event by instructingthe second control valve 45 to connect the valve actuation chamber 88 totank and thereupon the valve needle 61 returns to its seat and preventsfurther injection of fuel. Simultaneously or shortly thereafter, theelectronic control unit 25 instructs the first control valve 41 toconnect the actuation chamber 85 to tank. The pump chamber 82 isconnected to the pressurized source of low flashpoint fuel 30 and thesupply pressure of the low flashpoint liquid fuel that flows in via theone-way valve 89 urges the actuation piston 83 into the actuationchamber 85 until it has reached the position that is shown in FIG. 6with the pump chamber 82 completely filled with low flashpoint liquidfuel so that the fuel valve 50 is ready for the next injection event.FIG. 8 shows the position of the pump piston 80 and the actuationposition 83 near the end of an injection event with a major part of thepump chamber 80 depleted from low flashpoint fuel.

An injection event of the low flashpoint fuel is controlled by theelectronic control unit 25 by the timing and the duration of lift of thevalve needle 61. The electronic control unit can also control theinjection event by regulating the pressure supplied to the actuationchamber 85 in order to perform rate shaping.

The fuel valve 50 is provided with a sealing liquid inlet port 70 forconnection to a source of pressurized sealing liquid and provided with abore 94 extending from the sealing liquid inlet port 70 to the firstbore 81 for sealing the pump piston 80 in the first bore 81 in order toprevent the high-pressure fuel in the pump chamber 82 from leaking intothe space under actuation piston 83. In an embodiment, the pressure ofthe source of sealing liquid is at least as high as the maximum pressurein the pump chamber 82 during an injection event. In another embodimentthe pressure of the source of sealing liquid is at least as high as thesupply pressure of the low flashpoint fuel.

The sealing liquid is provided to the clearance between the longitudinalbore and the valve needle 61 via transverse bore 99 needs only to sealagainst the supply pressure of the fuel since the fuel inlet port 76 isconnected to a low-pressure fuel conduit 98 that extends from the fuelinlet port 76 through the elongated valve housing 52, through theintermediate section 53 into the nozzle body 55 and to the longitudinalbore in which the valve needle 61 is slidably received. The position atwhich the low-pressure fuel conduit 98 connects to the longitudinal boreis axially between the position where the fuel channels 79 connects tothe longitudinal bore and the position where the transverse bore 99connects to the longitudinal bore. Thus, any low flashpoint fuel leakingupwards (upward as in FIGS. 6 to 9)) through the clearance between thelongitudinal bore and the valve needle 61 from the high pressure fuelcavity 58 during an injection event will have its pressure reduced tothe much lower fuel feed pressure when it reaches the position where thelow-pressure fuel conduit 98 connects to the longitudinal bore. Thus,the low-pressure in the fuel conduit 98 “punctures” the pressure of thefuel in the clearance between the valve needle 61 and the longitudinalbore and thus, the sealing liquid from the transverse bore 99 needs onlyto seal against the feed pressure of the low flashpoint fuel and notagainst the injection pressure. Thus, the pressure of the sealing oilneeds only to be marginally higher than the feed pressure of the lowflashpoint fuel and does not need to be as high or higher than theinjection pressure of the fuel.

FIG. 10 shows an alternative type of nozzle 54 for use with the fuelvalve 50 described above with reference to FIGS. 5 to 9. In thisembodiment the nozzle 54 is of a so-called slider type in which thevalve seat 63 is arranged at a distance from the tip 56 of the nozzle 54and the tip 56 of the nozzle is in this embodiment closed, i.e. the tip56 does not have any nozzle holes. Instead, the nozzle holes arearranged along the length of the nozzle starting at a position close tothe tip 56 going upwards (upward as in the orientation of FIG. 10). Thevalve needle 61 is provided with a conical section that cooperates withthe valve seat 63 and a slider section that extends from the conicalsection of the valve needle 61 towards the tip of the valve needle 61.This type of nozzle with a closed tip and a slider of the valve needle61 extending inside the nozzle 54 towards the tip 56 is well known inthe art and will therefore not be described in any greater detail.

FIG. 11 is a flowchart illustrating a method according for injecting alow flashpoint fuel into the combustion chamber of a large two-strokecompression ignited internal combustion engine.

At the start of the method, block 101, the start time and the durationof the next fuel injection event is determined, for example by anelectronic control unit 25 of the engine. The electronic control unit 25determines the start time and duration of the injection on the basis ofvarious signals, such as e.g. engine load, engine speed, scavengingpressure and fuel properties.

Thereafter, block 102, the pressure booster 40 is started, e.g. by asignal from the electronic control unit 25 to the first control valve 41to change position, ahead of the planned start time of the fuelinjection event in order to give the pressure booster 40 time to buildup pressure in the relatively compressible low flashpoint fuel in thepump chamber. The change of position of the first control valve 41causes the actuation chamber of the pressure booster 40 for it to bepressurized and thereby pressurize the low flashpoint fuel in the pumpchamber of the pressure booster 40.

Next, block 103, the fuel valve 50 is opened at the determined starttime of the fuel injection event. This step can be carried out by theelectronic control unit 25 sending a signal to the second control valve45 to change position so that the needle actuation chamber 88 ispressurized, thereby lifting the valve needle 61.

The fuel valve 50 is closed, block 104, when the determined duration ofthe fuel injection event has been reached. Hereto, the electroniccontrol unit 25 issues a signal to the second control valve 45 to returnto the position where the needle actuation chamber 88 is connected totank, so that the valve needle 61 returns to its seat.

Simultaneously, or shortly thereafter, block 105, the electronic controlunit 25 issues a signal to the first control valve 41 to connect theactuation chamber of the pressure booster 42 tank, so that the pressurebooster 40 makes a return stroke, thereby refilling the pump chamber 82with low flashpoint fuel.

Thereupon, an injection event has been completed and the method cyclesback to block 101.

The signal cables mentioned above can be replaced by wirelessconnections. The actuation of the valve needle 61 under control of theelectronic control unit can be achieved in other ways than with ahydraulic control signal, such as e.g. with an electric actuator actingon the valve needle 61.

The present concept is not restricted to high compressibility fuels andneither to low flash point fuels. In practice the concept may offer mostadvantages when high compressibility of the fuel does not allow to letthe needle opening injection pressure control the lift of the needleitself.

The aspects have been described in conjunction with various embodimentsherein. However, other variations to the disclosed embodiments can beunderstood and effected by those skilled in the art in practicing theclaimed aspects, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. The mere fact that certain measures are recited inmutually different dependent claims does not indicate that a combinationof these measured cannot be used to advantage.

The invention claimed is:
 1. A large two-stroke turbochargedcompression-ignited internal combustion crosshead engine comprising: aplurality of cylinders, at least one pressure booster for each cylinderfor boosting fuel pressure, two or more electronically controlled fuelvalves for each cylinder with an inlet of said two or moreelectronically controlled fuel valves being connected to an outlet ofsaid at least one pressure booster, and with the opening and closing ofsaid electronically controlled fuel valves being independent from thepressure of the fuel supplied to the electronically controlled fuelvalves, an electronic control unit operably connected to said at leastone pressure booster and said two or more electronically controlled fuelvalves, said electronic control unit being configured to: determine astart time for a fuel injection event, activate said at least onepressure booster ahead of the determined start time, open the two ormore electronically controlled fuel valves at the determined start time.2. An engine according to claim 1, wherein said electronic control unitis configured to determine said start time for each cylinder of saidplurality of cylinders for each engine cycle.
 3. An engine according toclaim 1, wherein said electronic control unit is configured to activatethe at least one pressure booster ahead of the determined start time bya lead time with a length determined by said electronic control unit. 4.An engine according to claim 3, wherein said electronic control unit isconfigured use a fixed length lead time, a lead time length obtainedfrom a lookup table stored in said electronic control unit or a leadtime length determined by said electronic control unit using analgorithm stored in said electronic control unit.
 5. An engine accordingto claim 1, wherein said electronic control unit is configured todetermine the duration of a fuel injection event and wherein saidelectronic control unit is configured to close said at least twoelectronically controlled fuel valves at the end of said duration andconfigured to deactivate said at least one pressure booster at the endof said duration.
 6. An engine according to claim 1, wherein each fuelvalve comprises an elongated valve housing and wherein said pressurebooster is disposed inside said elongated valve housing, and whereinsaid pressure booster comprises a pump piston received in a first borein said valve housing with a pump chamber in said first bore on one sideof said pump piston, an actuation piston received in a second bore insaid valve housing with an actuation chamber in said second bore on oneside of said actuation piston, said pump piston being connected to saidactuation piston to move in unison therewith, said actuation chamberbeing connected to an actuation fluid port, said pump chamber having anoutlet connected to a fluidic connection to the nozzle holes of a nozzleof said fuel valve.
 7. An engine according to claim 1, wherein saidpressure booster and said fuel valve are configured to operate with alow flashpoint fuel.
 8. An engine according to claim 1, wherein saidpressure booster and said fuel valve are configured to operate with alow flashpoint fuel that is more compressible than fuel oil.